Ceiling fans have become increasingly popular in today's homes and businesses, such as restaurants. In the past, ceiling boxes, known as ceiling pans, for supporting the fans were tested under static loads only. With the increasing popularity of ceiling fans came the concern that the dynamic loads of an unbalanced ceiling fan could cause the mounting flanges of the ceiling boxes to flex and eventually break off. This concern lead to a new 1987 N.E.C. code provision (N.E.C. 370-17C) that required ceiling boxes intended to be used as the sole support of ceiling fans to be tested and listed for that use. Underwriters Laboratories (U.L.) responded with a new test which no ceiling box has yet been able to pass.
The prior art ceiling boxes are made of metal and have a pair of mounting flanges with a threaded mounting hole extending through each flange. In essence, these flanges are small ears formed integrally with the wall of the box and bent inwardly. The ceiling fan is attached to the ceiling box by a pair of mounting screws which are threadedly received in the mounting holes of the pair of flanges. Some prior art ceiling boxes have clearance holes in the top wall aligned with the mounting holes in the flanges to accommodate long mounting screws. These clearance holes neither provide support nor stabilize the mounting screws. Thus, the fan is merely supported and secured by the pair of mounting flanges extending from the ceiling box.
The problem with these prior art ceiling boxes is that the unbalanced dynamic loads cause the fan to rock back and forth, which in turn flexes and ultimately fatigues the flanges of the metal ceiling box until they break off.